The problem with pistol-grips VS. butthole stocks depends on 2 different laws.
1989- imported rifles could have NO evil items like flash suppressors, folding stock, pistol grips. The way that the law defined a "Pistol Grip" left open the possibillity of connecting the bottom, and POOF!!! It's no longer a pistol grip....it's a butthole stock!
But the 1994 law for domestic rifles defines a pistol grip with different terms, which make butthole stocks considered the same a pistol grips for US made rifles
So...
Thumbhole stocks count as an evil item on AR's, so try one of the other "non-pistol grip" thingys instead. ZM weapons makes one that looks like a hook. I plan to get one, but haven't yet.
As for the SAR 4800... Add enough US parts to that thing and you can ditch that butthole stock!!!